1. Field of the Invention
The present invention relates to a toner conveying device used to feed toner in an image forming apparatus including, for example, an image bearing member that forms a toner image on the surface thereof. The present invention also relates to a cleaning device for cleaning the surface of the image bearing member, including the toner conveying device, and to an image forming apparatus using the toner conveying device or the cleaning device.
2. Description of the Related Art
Conventionally, a developing device of an image forming apparatus uses a toner conveying device for feeding toner. The toner conveying device includes, for example, a tubular conveying pipe having an inner diameter that gradually decreases from the upstream side toward the downstream side and a conveying screw that is concentrically arranged in the conveying pipe so as to be rotatable.
The inside and outside diameters of the conveying pipe gradually decrease toward the downstream side. In this structure, toner fed through the conveying pipe toward the downstream side is compressed, on the downstream side, due to the rotation of the conveying screw about the axis. Friction caused by the compression charges the carrier, which is made of synthetic resin and is located in the toner, increasing the charge level of the toner deposited on the carrier. This increase in the charge level creates a smooth toner image on the circumferential surface of the photosensitive drum.
Furthermore, conventionally, it is known to use as a toner conveying device in the developing device of the image forming apparatus, a toner conveying device that has a conveying screw for feeding toner in a housing, a portion of the conveying screw corresponding to a toner supply port in the housing having an outside diameter that is slightly larger than that of the other portions or a screw pitch that is slightly larger than that of the other portions. This structure increases the feeding speed of the toner near the toner supply port when the toner is supplied to the developing device through the toner supply port, thereby preventing the toner from staying. Thus, the supply of toner to the device is smoothly performed.
In this type of toner conveying device, both the inside diameter of the conveying pipe and the outside diameter of the conveying screw gradually decrease toward the downstream side. However, the purpose of such a structure is not to prevent toner from sticking to the inner wall surface of the pipe or to make the amount of toner fed uniform, but to compress the toner on the downstream side to increase the charging level.
In these toner conveying devices, the conveying screw has a large diameter only near the toner supply port of the housing of the developing device. Countermeasures against toner sticking to the bottom of the housing at other portions or to achieve a uniform conveyance of toner are not considered by these devices. Therefore, there is a problem in that toner may deposit on and stick to the bottom of the housing on the upstream side of the toner supply port, making a smooth conveyance of toner difficult.